Bump travis dist version

.travis.yml

@@ -1,6 +1,6 @@
 language: node_js
 sudo: required
-dist: trusty
+dist: xenial
 addons:
     chrome: stable
 node_js:
@@ -11,6 +11,7 @@ env:
   - SMOKE_URL=https://llk.github.io/scratch-gui/$TRAVIS_PULL_REQUEST_BRANCH
   - NPM_TAG=latest
   - RELEASE_VERSION="0.1.0-prerelease.$(date +'%Y%m%d%H%M%S')"
+  - CHROMEDRIVER_VERSION=LATEST
 cache:
   directories:
   - node_modules